Conventionally, as an exhaust gas-purifying catalyst that treats an exhaust gas of an automobile, a three-way catalyst with a precious metal such as platinum supported by an inorganic oxide such as ceria or alumina has been widely used. In the three-way catalyst, the precious metal plays the role in promoting the reduction of nitrogen oxides and the oxidations of carbon monoxide and hydrocarbons. The inorganic oxide plays the roles in increasing the specific surface area of the precious metal and suppressing the sintering of the precious metal by dissipating heat generated by the reactions.
In recent years, occasions when an automotive vehicle such as an automobile is driven at high-speed increase as the performance of an engine increases. Additionally, in order to prevent the pollution of the air, the regulations on the exhaust gas are made more stringent. Against these backdrops, temperature of the exhaust gas emitted by the automotive vehicle is on the trend of rising. For that, in order to achieve the exhaust gas-purifying catalyst that exhibits sufficient performance even when being used under such a condition, research and development are actively carried out.
For example, Jpn. Pat. Appln. KOKAI Publication No. 1-242149 describes NiAl2O4 generated during the reaction of alumina supporting a precious metal with nickel at high temperatures when nickel is used in order to remove hydrogen sulfide from an exhaust gas. The NiAl2O4 has a spinel structure. The Patent Literature describes large deterioration in the activity of a catalyst during the reaction. Furthermore, the Patent Literature describes the effective use of a composite oxide containing ceria and zirconia for the suppression of the reaction.
Jpn. Pat. Appln. KOKOKU Publication No. 6-75675 describes the grain growth of ceria when being used at high temperatures, which causes deterioration in oxygen storage capacity. The Patent Literature describes the grain growth of a composite oxide represented by a general formula Ce1−xLaxO2−x/2 when being used at high temperatures, which causes deterioration in purification performance. The composite oxide has a fluorite structure. Furthermore, in the Patent Literature, the following are described. Even when a composite oxide or a solid solution that contains zirconia and ceria, wherein the atomic ratio of zirconium and cerium is 5/95 to 70/30, is used at high temperatures, the grain growth of the composite oxide or the solid solution is less likely to occur.
Jpn. Pat. Appln. KOKAI Publication No. 10-202101 describes a support containing alumina, ceria, and zirconia uniformly dispersed and having high heat resistance.
Jpn. Pat. Appln. KOKAI Publication No. 2004-41866 describes a composite oxide having a perovskite structure represented by a general formula ABPdO3. In the general formula, the element A is at least one rare-earth element such as La, Nd, and Y that exhibits a valence of 3 and cannot exhibit other valences. The element B is at least one element selected from the group consisting of Al and transition elements other than Co, Pd, and rare-earth elements. The Patent Literature describes the catalyst activity of palladium maintained at a high level for a long period of time when the composite oxide is used.
Jpn. Pat. Appln. KOKAI Publication No. 2004-41867 describes a composite oxide having a perovskite structure represented by a general formula ABRhO3. In the general formula, the element A is at least one rare-earth element such as La, Nd, and Y that exhibits a valence of 3 and cannot exhibit other valences, or a combination of such a rare-earth element and at least one of Ce and Pr. The element B is at least one element selected from the group consisting of Al and transition elements other than Co, Rh, and rare-earth elements. The Patent Literature describes the catalyst activity of rhodium maintained at a high level for a long period of time when the composite oxide is used. Jpn. Pat. Appln. KOKAI Publication No. 2004-41868 describes a composite oxide having a perovskite structure represented by a general formula A1−xA′xB1−y−zB′yPtzO3. In the general formula, the element A is at least one rare-earth element such as La, Nd, and Y that exhibits a valence of 3, and cannot exhibit other valences. The element A′ is at least one element selected from an alkaline-earth metal and Ag. The element B is at least one element selected from Fe, Mn, and Al. The element B′ is at least one element selected from transition elements other than Pt, Fe, Mn, Co, and rare-earth elements. The Patent Literature describes the catalyst activity of platinum maintained at a high level for a long period of time when the composite oxide is used.